1. Field of the Invention
This invention relates to elastomeric balloons that are filled with gas which can be lighter than air, such as helium. More specifically, this invention relates to a method for treating inflatable elastomeric balloons to increase their buoyant lifetime.
2. Description of the Prior Art
Small toy balloons having an inflated diameter ranging from about 15 cm to about 50 cm are conventionally made by filling a brightly colored elastomeric envelope with helium gas. Such lighter than air balloons have been widely sold and used for a number of years at places like circuses, fairs, toy stores, and the like. Another common use for such balloons is for advertising purposes wherein a logo or advertising message is printed on the outside surface of the balloon. In more recent years there has been a proliferation of balloon greeting serive companies who, for a fee, deliver bunches of helium inflated elastomeric balloons, usually conveying a personal message, to individuals on birthdays, anniversaries, Valentines Day, or other special occasions. Another popular use for this balloon delivery service is to send a get well message with up to a dozen helium inflated balloons to an adult or child who is convalescing from an illness in a hospital or other institution. A major problem with such prior art helium filled elastomeric balloons is that they do not remain buoyant for very long; their typical buoyant lifetime ranges from a few hours to a day or so. This short buoyant lifetime is due to the diffusion of the very small helium atoms through the elastomeric envelope provided by the balloon. Because of the short buoyant lifetime, such balloons must be inflated at the time of sale or just piror to sale. They cannot be inflated in advance and stocked for use when needed.
Accordingly, over the years various attempts have been made to develop envelope materials for lighter than air balloons which have decreased permeability to inflation gasses such as helium. Methods have been developed for making large meteorological and aeronautical balloons having volumes of 3000 L. or more which have very long buoyant lifetimes. Due to the small surface-to-volume ratio of such large balloons, the envelope materials can be made relatively thick and heavy without affecting their long term buoyancy. For example, methods for making laminated envelopes for meteorological and aeronautical balloons wherein one or more gas impermeable layers, typicall metal sheet or foil, are used in combination with layers of cloth, rubber, cellulose, paper, or leather are disclosed in German Pat. Nos. 219,440; 224,521; 227,150; 515,083; and U.S. Pat. Nos. 1,793,075 and 1,801,666. Again, the thick walled envelopes resulting from these methods have a relatively high weight per unit of surface area and cannot be successfully scaled down to the smaller size of typical toy and advertising balloons.
U.S. Pat. Nos. 3,149,017 and 3,608,849 disclose using non-elastic materials such as biaxially oriented polyethylene in making the envelopes for large meteorlogical balloons. Again, the thick wall required for satisfactory retention of helium rules out its use in the smaller toy and advertisting balloons.
A recent attempt to solve the problem of short buoyant lieftime of small balloons is disclosed in U.S. Pat. No. 4,077,588 wherein the balloon envelope is fabricated from a seamed panel of nonelastic polymer having a vapor deposited metal coating. Experience in using balloons manufactured by this method, commonly known as "Mylar".TM. (DuPont Co.) balloons, has revealed a number of serious problems. Typically, "Mylar" balloons cost about 10 times as much as elastomeric balloons of equivalent size. Since the "Mylar" balloons are nonelastic, they are inflated with helium to about atmospheric pressure; even a slight overinflation causes the seams to rupture since these balloons cannot expand elastically. Morover, these balloons are extremely temperature sensitivie. A "Mylar" balloon inflated at room temperature often generates sufficient internal pressure to rupture the seam if the balloon is moved to a location where the temperature is warmer such as out of doors on a warm day. Similarly, a "Mylar" balloon inflated at room temperature will deflate partially and become non-buoyant when moved to a cooler location. Another problem with the "Mylar" balloon is that it must be heat sealed after inflation; this is a time consuming step requiring special equipment and can be expensive.
U.S. Pat. Nos. 2,646,370 and 3,415,767 disclose methods for plasticizing neoprene synthetic rubber used in making meteorological balloons in order to improve the low temperature elastic properties at high altitudes.